Ah! I've been wanting something like this for a notebook I'm working on, but I've had no idea how to make it. I'll poke around and see how you put it together. Exciting to find this, and of course this whole notebook is great too. Thank you.

Glad this helps for your notebook! The original cell is imported from another of my notebooks: https://observablehq.com/@daformat/rounding-polygon-corners feel free to re-use / improve / clean :)